Assembly lines where adhesive is applied to an advancing line of cardboard, paper, thin plastic blanks, or the like are very commonplace. The adhesive is dispensed from an automated applicator head. The blanks are subsequently manipulated to create a container or other manufactured article.
In some applications, a wide band of adhesive needs to be applied to the moving substrate. Known processes for this purpose utilize extruding, spraying, roll coating and swirling techniques. All such processes have their advantages and disadvantages as explained below.
The extruding process forces the adhesive, under pressure, onto the substrate. A nozzle selected for a desired adhesive band width or thickness is chosen according to need. The process usually is done with the nozzle contacting the substrate. This tends to concentrate the adhesive deposit, which limits its spreadability. It also causes wear to the nozzle and can lead to frequent cleaning of its tip and associated apparatus. Most importantly, the volume of adhesive applied by the contact extrusion process is very difficult to control, resulting in over/under adhesive applied products. This, in turn, results in lack of cost control and quality control.
In the spraying process, there is no contact with the substrate as the adhesive is sprayed onto it through a nozzle. But the adhesive is very fast drying due to air atomization and, therefore, has less open time. Also, air atomization can cause a mess on the equipment itself and wastes material due to airborne misting of small adhesive particles. The pattern width of applied adhesive will vary with the nozzle height over the substrate. Adjusting the height gives the user a certain degree of band control, but it increases machine setup time.
The roll coating process contacts the substrate with a coated roll. By the very nature of the process, the adhesive needs to be applied in a thin layer. This increases the adhesive surface to air ratio which in turn speeds the curing process. The precision design of the machine makes it relatively expensive and is less adaptive to selecting various adhesive band widths. Also, adhesive is wasted and much clean-up is required.
In the swirling process, a dispensing valve does not contact the substrate. Rather, it produces a tight circular pattern. This pattern produces uneven dispensing as it produces heavy pattern lines on the outside dimension of the swirl in the direction of the automated product or applicator movement. The swirling process can also lead to an uneven start/stop pattern.
Effectively applying an adhesive in the needed wide pattern manner has been accomplished, but not without inherent problems as noted. There has now been developed an adhesive applicator head which applies a wide band of adhesive to a moving substrate without substrate contact and its inherent problems. The width of the adhesive band is readily controlled. Most importantly, the applicator head of the invention is self-sealing during line stoppage and self-cleaning after a prolonged line stoppage.